McEntire performed "The Lord's Prayer" during the service which took place at the St. Martin's Episcopal Church in Houston.
The Oak Ridge Boys sang "Amazing Grace," a song the band said was Bush's favorite.
"President Bush means so much to us," band member Richard Sterban told The Tennessean. "George Bush requested before he passed away that we sing 'Amazing Grace,' his favorite song, at his funeral. There's no way we wouldn't do it."
"He always taught us to do the right thing, and it is a tremendous honor. One final time here on this earth, we're going to sing it for him and we believe in our hearts we'll see him again one day and we'll sing it for him again," Sterban continued.
McEntire, like The Oak Ridge Boys, had a friendship with Bush. The country star posted on Instagram following Bush's death a photo of herself sitting next to the former president while holding his hand. "My favorite. #greatpresident #greatfriend," she captioned the image.
Bush died Friday at the age of 94. His death came six months after the passing of his wife of 73 years, former first lady Barbara Bush.
Bush will be buried at the George Bush Presidential Library and Museum in College Station, Texas, next to his wife and daughter Robin, who died of leukemia in 1953 at the age of 3.